Printed circuit (PC) boards are used to electrically interconnect the many electronic components of an electronic circuit. A typical PC board includes an insulating substrate, usually made from a resinous plastic, and a number of conductive metal paths or "traces" for carrying power and signals between the various components of the circuit.
Many electronic systems divide their circuitry among a number of individual PC boards, and thus require an effective means for coupling the boards together. The most commonly used type of interconnect for this purpose is an "edge connector" which engages an edge of a PC board to contact pads formed thereon.
While edge connector technology is adequate when the number of required interconnects is small, problems arise as the interconnect requirements increase. For example, with edge connectors all connection must be made at the edges of the PC board, which requires the PC board designer to route the desired signals through the maze of components to the periphery of the PC board. This requirement may result in a less-than-optimal layout of the components and increase the size of the PC board, thereby possibly reducing the performance of the electronic circuit. Furthermore, since the contact pads of the PC board must be made sufficiently large to ensure adequatecontact with the edge connectors and must be sufficiently spaced to prevent shorts, the contact density of the edge connector technology is quite low, i.e. approximately eight contacts/cm. Also, since the contact pads are linearly arranged along board edges, the length of the edge connector in direct proportion with the number of signals to be routed off-board. This, in itself, can cause reliability problems, because PC boards tend to warp, which may cause poor contact between some of the contact pads and the edge connector as the length of the edge connector increases.
Due to the aforementioned limitations of edge connectors, a number of interconnect structures have been devised for more efficiently interconnecting PC boards. For example, in U.S Pat. No. 4,125,310, of Reardon, et al., an interconnect structure is disclosed which interconnects wire cables from PC boards or electrical components with a pair of chemically milled, thin metallic wafers. One of the wafers is plated with metallic buttons, while the other wafer is plated with contact pads. The two wafers are placed together and then compressed to force the metallic buttons into firm contact the contact pads of the adjoining wafer. This "metal button" technology permits two dimensional interconnections of approximately sixteen-hundred contacts/cm.sup.2.
Another interconnect structure is disclosed in U.S. Pat. No. 4,581,679 of Smollev which teaches an insulated board provided with a plurality of openings, and a number of connector elements comprising compressible wads of conductive wire which are lodged within selected openings of the insulated board. The insulated board is sandwiched between a pair of PC boards, thereby pressing the connector elements into contact with PC board contact pads to electrically couple the PC boards together. The structure described in the Smollev patent will permit two dimensional interconnections at a density of approximately twenty-five lines/cm.sup.2.
Electronic and electrical components can be attached to a PC board in a variety of ways, the most common of which is the provision of a number of predrilled contact pads which are receptive to leads of the components. Once the leads are engaged with the PC board holes, they are soldered to the pads to form a semi-permanent electrical connection with the PC board.
A higher density method for interconnecting an electronic component to a PC board involves the use of "surface mount technology" where the leads from the electronic components are soldered directly to the surface of pads on the PC board without being inserted into drill-holes. Surface mount technology permits an interconnection density which is approximately a factor of two greater than that of conventional, through-the-board mounting technology, allowing the manufacture of smaller, higher performance PC boards.
Other IC to PC board connection technologies include tape automated bonding (TAB) technology, and "solder bump" technology. With tape automated bonding, a tape provided with conductive traces is ultrasonically bonded to contact pads on the IC and the PC board, resulting in an interconnect density of approximately 20 contacts/cm.
With solder bump technology, an IC is turned over or "flipped" and solder bumps are provided on its active surface for direct bonding to contacts on a PC board or on another IC. While the solder bump technology is currently the most dense, commercially available interconnect technology with a two dimensional interconnect capacity of approximately twenty-five hundred contacts/cm.sup.2, it suffers from the disadvantage that, due to thermal expansion problems, the ICs with which it is used must be quite small. Also, the non-compliant nature of the solder bumps has the result of supporting the various IC's at different heights. Because the IC's usually must be liquid cooled to enhance their heat dissipation, the non-planarity of the IC's requires elaborate and expensive cooling systems. Furthermore, solder bump mounted IC's are difficult to assemble and repair. For these and other reasons, solder bump technology remains very expensive, and only desirable for the most demanding of applications.
What the related art does not disclose, then, is an interconnect structure for electrically interconnecting PC boards, ICs, and ICs to PC boards, which has a high contact density and compliance, which can be assembled and disassembled easily, and which is an economically feasible alternative to conventional interconnect structures.